The present invention relates generally to turbines and particularly to land-based industrial turbines for generation of electricity. More particularly, the present invention relates to a gas turbine having inner and outer turbine shells and support pins between the shells for securing the shells to one another while enabling thermal expansion and contraction in radial and axial directions.
In prior U.S. Pat. No. 5,685,693 of common assignee herewith, there is illustrated an industrial gas turbine having inner and outer shells. The inner shell has a pair of axially spaced circumferential arrays of radially outwardly projecting pins terminating in reduced sections having flats on opposite circumferential sides thereof. Generally cylindrical sleeves project inwardly and about access openings in the outer shell and have threaded bolt holes extending in circumferential directions. Bolts extend through the holes to engage the flats on the sides of the pins. By adjusting the bolts, the inner shell is adjustable externally of the outer shell to locate the inner shell about the rotor axis. Reference is made to that patent for a further, more detailed description of the inner shell/outer shell mounting arrangement. There has, however, developed a need for a more advanced mounting arrangement between the inner and outer shells in an advanced gas turbine design of assignee.
In accordance with a preferred embodiment of the present invention, axially spaced forward and aft arrays of circumferentially spaced support pins secure the inner shell to the outer shell of the turbine in a manner which supports the inner shell against radial and circumferential movement relative to the outer shell and enables thermal expansion and contraction of the inner shell relative to the outer shell in radial and axial directions. The support pins are loaded only in circumferential or tangential directions and do not carry loads in radial or axial directions. Moreover, the weight of the inner shell is likewise carried in a circumferential direction. To accomplish the foregoing and obtain other benefits and advantages, and in a preferred embodiment, the present invention provides support pins each comprised of a cylindrical head containing a bolt circle, a generally cylindrical shank and a reduced radially inwardly extending projection for engaging the inner shell. The support pins for the forward and aft portions of the inner shell are substantially similar in configuration to one another. Each projection of each support pin has opposite sides facing in opposite circumferential directions. The sides are arcuate about axes extending generally parallel to the rotor axis. The projection is also rectilinear in radial cross-section and has flat opposite end faces in the fore and aft directions.
Preferably, a pair of axially spaced arrays of circumferentially spaced recesses are provided about forward and aft portions of the inner shell. The recesses are rectilinear and open radially outwardly of the shell. The support pins are bolted to the outer shell and are received through access openings in the outer shell. The inner projections are received in the recesses. The arcuate side faces of each projection forms a line contact with circumferentially facing side walls of the recesses. The opposed axial end faces of the projection, however, are spaced from the end walls of the recesses, enabling axial movement of the inner shell to accommodate thermal expansion and contraction.
The recesses in the rim of the inner shell comprise rectilinear through-openings formed in bushings. The bushings are circular and are received in circular openings formed in the inner shell. These rectilinear recesses are preferably formed in the bushings by an EDM process. This facilitates manufacture of the inner shell.
In a preferred embodiment according to the present invention, there is provided a turbine comprising an outer structural shell, an inner shell connected to and surrounded by the outer shell in generally concentric relation therewith, the inner shell carrying nozzles and shrouds for a turbine stage, the shrouds surrounding tips of buckets carried by a turbine rotor within the inner shell, a plurality of connecting elements engaging between the inner and outer shells aligning the inner shell about the rotor, the connecting elements engaging the inner shell with a clearance in an axial direction of the rotor to enable differential growth of the inner shell relative to the outer shell in an axial direction while maintaining concentricity of the inner shell about the rotor.
In a further preferred embodiment according to the present invention, there is provided a turbine comprising an outer structural shell, an inner shell connected to and surrounded by the outer shell in generally concentric relation therewith, the inner shell carrying nozzles and shrouds for a turbine stage, the shrouds surrounding tips of buckets carried by an axially extending turbine rotor within the inner shell, a plurality of connecting elements engaging between the inner and outer shells aligning the inner shell about the rotor, each of the connecting elements including a radial inward projection, the inner shell having a plurality of recesses spaced circumferentially thereabout receiving the projections of the connecting elements.